#include <Eigen/Core>
#include <iostream>
using namespace Eigen;
using namespace std;

template<typename Derived>
Eigen::VectorBlock<Derived>
segmentFromRange(MatrixBase<Derived>& v, int start, int end)
{
	return Eigen::VectorBlock<Derived>(v.derived(), start, end - start);
}

template<typename Derived>
const Eigen::VectorBlock<const Derived>
segmentFromRange(const MatrixBase<Derived>& v, int start, int end)
{
	return Eigen::VectorBlock<const Derived>(v.derived(), start, end - start);
}

int
main(int, char**)
{
	Matrix<int, 1, 6> v;
	v << 1, 2, 3, 4, 5, 6;
	cout << segmentFromRange(2 * v, 2, 4) << endl; // calls the const version
	segmentFromRange(v, 1, 3) *= 5;				   // calls the non-const version
	cout << "Now the vector v is:" << endl << v << endl;
	return 0;
}
